CONTENTS

CERTIFICATE
ACKNOWLEDGEMENT
CHAPTER

TITLE

1.

INTRODUCTION

2.

BLOCK DIAGRAM

3.

MATRIAL DESCRIPTION

4.

MATRIAL LIST

5.

MATRIAL DESCRIPTION

6.

REFERENCES

1
INTRODUCTION

INTRODUCTION

Auto stoping of rotating cutting blade is a machine which can be

used for industrial applications and Household needs in which no
specific input energy or power is needed. This project consists of a
ir sensor and rotating blade. In the mechanism ir sensor is directly
connected to the rotating cutting blade through relay for the
processing of cutting the wooden blocks stop. The objective of the
modal is to stop the rotating blade.
The power rotating cutting blade machine, which runs on human
presence, works on the principle of the sensing the concentration
of human being , if person not concentrate the sensing device
automatically stop the cutting machine.
Application

Metal or wood cutting.

BLOCK
DIAGRAM

BLOCK DIAGRAM
Ldr sensor

relay

Circuit diagram

Working
The automatic cutter machine control system operates on 12 V DC supply. The automatic
cutter machine control has a photoconductive device whose resistance changes proportional
to the extent of illumination, which switches ON or OFF the motor with the use of transistor
as a switch.
Light dependent resistor, a photoconductive device has been used as the transducer to convert
light energy into electrical energy.
The central dogma of the circuit is that the change in voltage drop across the light dependent
resistor on illumination or darkness switches the transistor between cut-off region or
saturation region and switches OFF or ON the LEDAs we know property of LDR that during
the time of day resistance is low therefore voltage at the inverting input ( IE pin 2) is higher
than the voltage at the non-inverting input (pin3) hence the output at the pin6 is low so the
transistor goes into the cut off state which means MOTOR will not glow.

MATERIAL

DESCRIPTION

MATERIAL DESCRIPTION
1) DC Motor
DC motor is an electric motor that runs on direct current (DC) electricity. DC
motors were used to run machinery, often eliminating the need for a local steam
engine or internal combustion engine. DC motors can operate directly from
rechargeable batteries, providing the motive power. Modern DC motors are
nearly always operated in conjunction with power electronic devices.

2) Aluminum Strip
Sheet
into

thin

metal is
and

flat

with holes
simply metal formed
pieces. It is one of

the fundamental forms used in metalworking, and can be cut and bent into a
variety of different shapes. Countless everyday objects are constructed of the

material. Thicknesses can vary significantly, although extremely thin thicknesses

are considered foil or leaf, and pieces thicker than 6 mm (0.25 in) are
considered plate. And holes were cut by blanking process in an organized
manner

3) Power supply
This consist a

12V power supply

source through DC adopter.

4) Square tube
Hollow square tube, which have a uniform cross-section with only one
enclosed void along their whole length in the shape of rectangles (including
squares), and which have a uniform wall thickness.
5) Cutter:A cutting

blade is

under tension in

fine-tooth

frame,

hand

used

saw

with

a blade held

for cutting materials

such

as metal or plastics. Hand-held cutting blades consist of a metal arch with a

handle, usually a pistol grip, with pins for attaching a narrow disposable
blade. A screw or other mechanism is used to put the thin blade under
tension. The blade can be mounted with the teeth facing toward or away from
the handle, resulting in cutting action on either the push or pull stroke. On the
push stroke, the arch will flex slightly, decreasing the tension on the blade,
often resulting in an increased tendency of the blade to buckle and crack.
Control of the cut and longer blade life.

6) Nut bolt
In normal use, a nut-and-bolt joint holds together because the bolt is under
a constant tensile stress called the preload. The preload pulls the nut
threads against the bolt threads, and the nut face against the bearing surface,
with a constant force, so that the nut cannot rotate without overcoming
the friction between these surfaces. If the joint is subjected tovibration,
however, the preload increases and decreases with each cycle of movement.
If the minimum preload during the vibration cycle is not enough to hold the nut
firmly in contact with the bolt and the bearing surface, then the nut is likely to
become loose.

7) Switches
DPDT (double pole, double throw): A DPDT switch routes two separate
circuits, connecting each of two inputs to one of two outputs. A DPDT switch
has six terminals: two for the inputs, two for the A out puts, and two for the B
outputs.

8) Plywood
Plywood layers (called veneers) are glued together, with adjacent plies
having their wood grain at right angles to each other, to form acomposite
material. This alternation of the grain is called cross-graining and has several
important benefits: it reduces the tendency of wood to split when nailed at the
edges; it reduces expansion and shrinkage, providing improved dimensional
stability; and it makes the strength of the panel consistent across both
directions. There is usually an odd number of plies, so that the sheet is
balancedthis reduces warping. Because plywood is bonded with grains
running against one another and with an odd number of composite parts, it is
very hard to bend it perpendicular to the grain direction.

MATERIAL
LIST

MATERIAL LIST:1) DC Motor

2) Aluminum Strip with holes
3) Square tube
4) Cutter blade
5) Nut bolt
6) Switches
7) Plywood
8) Power supply block
9) Ldr
10) Relay

MATERIAL
DESCRIPTION

MATERIAL DESCRIPTION
DC MOTORS:
Basically, the motors can be categorized into two parts, AC and
DC. The basic principle of operation is almost same. In any electric
motor, the operation is based on simple electromagnetism. A current
carrying conductor generates a magnetic field; when this is placed in
an external magnetic field, it will experience a force proportional to
the current in the conductor, and the strength of the external magnetic
field.

The

internal

configuration

of a DC motor

is designed to harness

the

interaction between a

magnetic

current carrying

conductor

and

an

external magnetic field to generate rotational motion.

DC Motors can
1.

Externally

This type of DC

be classified as:
Excited DC Motor:
motor is constructed such

that the field is not connected to the armature. This type of DC motor
is not normally used

2. Shunt DC Motor:
The motor is called a "shunt" motor because the field is in parallel, or
"shunts" the armature. This type of motor runs practically constant
speed, regardless of the load. It is the type generally used in
commercial practice and is usually recommended where starting
conditions are not usually severs. Speed of the shunt-wound motors
may be regulated in two ways: first, by inserting resistance in series
with the armature, thus decreasing speed: and second, by inserting
resistance in the field circuit, the speed will vary with each change in
load: in the latter, the speed is practically constant for any setting of
the controller. A shunt wound motor has a high-resistance field
winding

connected in parallel with

the armature.

It responds to increased

load by trying

to maintain its speed and

this leads to

an increase in armature

current. This makes it unsuitable for widely-varying loads, which may

lead to overheating.

3. Series DC Motor:
The motor field windings for a series motor are in series with the
armature.
This type of motor speed varies automatically with the load,
increasing as the load decreases. Use of series motor is generally

limited to case where a heavy power demand is necessary to bring

the machine up to speed, as in the case of certain elevator and hoist
installations, for steel cars, etc. Series-wound motors should never be
used where the motor can be started without load, since they will race
to a dangerous degree. A series wound motor has a low-resistance
field winding connected in series with the armature. It responds to
increased load by slowing down and this reduces the armature
current and minimizes the risk of overheating.
4. Compound DC Motor:
A compounded DC motor is constructed so that it contains both a
shunt and a series field. This particular schematic shows a
cumulatively-compounded" DC motor because the shunt and series
fields are aiding one another combination of the shunt wound and
series

wound

types

combines

the

characteristics

of

both.

Characteristics may be varied by varying the combination of the two

windings. These motors are generally used where severe starting
conditions are met and constant speed is required at the same time.
Speed control:
Generally, the rotational speed of a DC motor is proportional to the
voltage applied to it, and the torque is proportional to the current.
Speed control can be achieved by variable battery tapings, variable
supply voltage, resistors or electronic controls.
In a circuit known as a chopper, the average voltage applied to the
motor is varied by switching the supply voltage very rapidly. As the
"on" to "off" ratio is varied to alter the average applied voltage, the
speed of the motor varies. The percentage "on" time multiplied by the
supply voltage gives the average voltage applied to the motor.
Therefore, with a 100 V supply and a 25% "on" time, the average
voltage at the motor will be 25 V. During the "off" time, the armature's

inductance causes the current to continue through a diode called a

"fly back diode", in parallel with the motor. At this point in the cycle,
the supply current will be zero, and therefore the average motor
current will always be higher than the supply current unless the
percentage

"on"

time is 100%. At 100%

time,

the

supply and motor current

are

equal.

The

rapid

less

energy

than

series

"on"

switching

wastes

resistors.

This

method is also called pulse-width modulation (PWM) and is often

controlled by a microprocessor. An output filter is sometimes installed
to smooth the average voltage applied to the motor and reduce motor
noise.

DC

MOTOR
DRIVER:
As the

most

the

PORT

of

or

any

other

of

MCU

controlling ICs are not powerful enough

to drive DC motors directly so we need some kind of drivers. A very
easy and safe is to use popular L293D chips. It is a 16 PIN chip. The
pin configuration is shown in the diagram.

This chip is designed to control 2 DC motors. There are 2

INPUT and 2 OUTPUT pins for each motor. The diagram with proper
connection is shown in the next diagram. The RA3 and RA2 pins
are used to control the motor one and RA0 and RA1 pins are used
to control motor B. Pin1 and Pin9 are enable pins. If these pins are
not connected to +5V, then both the drivers will remain deactivated
until they are enabled. Whatever power supply we provide at pin 8
and pin 16, this supply will go to both motors. Hence we have to be
careful about the rating of motors while connecting the power supply
to this IC using this IC.
The behavior of both motors are similar are exactly similar.
Here the table describes the controlling method of one motor; same is
applicable for other motor.
Signal

at Signal

RA3
LOW
LOW
HIGH
High

RA2
LOW
HIGH
LOW
High

at Rotation of Motor A
Stop
clockwise
Anticlockwise
Stop

From the above discussion it is clear that the motor can be stopped in
two ways, either by sending ground signal to both controlling lines, or
by sending high on both signal pins. If we have to stop the motor
immediately, then we should send high on both signal pins. This is
known as active braking, by which the motor is stopped instantly.
The basic idea behind controlling any DC motor is explained below;
this circuit arrangement is known as H Bridge because it looks like an
H. The circuit diagram for H Bridge is shown. In general an H bridge
is a rather simple circuit, containing four switching elements with the

load at the center, in an H like configuration. The switching elements

(Q1.Q4), are usually bi-polar or FET transistors, in some highvoltage applications IGBTs. In fact the similar arrangement is present
in our L293D IC. The operation of the circuit is very easily understood
by the following diagram.
The

basic

operating

mode of an H-

bridge

is

simple: if Q2

and Q3 are turned

on,

left

lead of the motor

be

connected

the

will
ground,

while

connected

fairly

to

the right lead is

to

the power supply.

Current starts

flowing through the

motor

energizes

which

the

motor in (let's say) the forward direction and the motor shaft starts
spinning. If Q1 and Q4 are turned on, the converse will happen, the
motor gets energized in the reverse direction, and the shaft will start
spinning in that way.

The role of cathode diodes is explained below:

The basic principle is very simple: while the bridge is on, two of the
four switching elements will carry the current, the diodes have no
role. However once the bridge is turned off the switches will not
conduct current any more. As discussed earlier, by far the most
common load for an H-bridge is an electric DC motor, which is an
inductive load. What this means is that during the on-time the motor
will build an electromagnetic field inside it. When the switch is turned
off, that field has to collapse, and until that happens, current must still
flow through the windings. That current cannot flow through the
switches since they are off, but it will find a way. The catch diodes are
in the design to provide a low-resistance path for that collapse current
and thus keep the voltage on the motor terminals within a reasonable
range.
Aluminum Strip with holes
Marsden Matting is standardized, perforated steel matting material
originally developed by the United States at the Waterways Experiment Station
shortly before World War II, primarily for the rapid construction of temporary
runways and landing strips. The material is also commonly known as Marston
mats (or Marston Plate) for a town in North Carolina adjacent to Camp Mackall
airfield where the material was first manufactured [1] and used in November 1941.
[2]

The material was also used in the Korean and Vietnam Wars where its

common name, from its NATO Stock Number nomenclature, is pierced (or
perforated) steel planking (PSP). Marsden matting consisted of steel strips
with holes punched through it in rows and a formation of U-shaped channels

between the holes. Hooks were formed along one long edge and slots along the
other long edge so that they could be connected to each other. The short edges
were straight cut with no holes or hooks. To achieve lengthwise interlocking, the
mats were laid in a staggered pattern. The hooks were usually held in the slots
by a steel clip that filled the part of the slot that is empty when the adjacent
sheets are properly engaged together. The holes were bent up at their edges so
that the beveled edge stiffened the area around the hole. In some mats a Tshaped stake could be driven, at intervals, through the holes to keep the
assembly in place on the ground. Sometimes the sheets were welded together.
The typical Marsden matting was the M8 landing mat. A single piece weighed
about 66 pounds and was 10 ft (3.0 m) long by 15 in (0.38 m) wide. The hole
pattern for the sheet was three holes wide by 29 holes long resulting in 87 holes
per mat. A variation made from aluminum was produced to allow easier
transportation by aircraft, since it weighed about 2/3 as much. It was referred to
as PAP for perforated aluminum planking, [3] but was not as common as
aluminum was a controlled strategic material during World War II. PSP was later,
after the war, used by many early southeastern U.S. auto racing teams as it was
manufactured in the area, and used in many abandoned military airfields. It was
also used during a similar period when NASCAR teams used car trailers.

DPDT Switch
In electrical engineering, a switch is an electrical component that can
break an electrical circuit, interrupting the current or diverting it from one
conductor to another. The most familiar form of switch is a manually operated
electromechanical device with one or more sets of electrical contacts, which are
connected to external circuits. Each set of contacts can be in one of two states:
either "closed" meaning the contacts are touching and electricity can flow
between them, or "open", meaning the contacts are separated and the switch is
nonconducting. The mechanism actuating the transition between these two
states (open or closed) can be either a "toggle" (flip switch for continuous "on" or
"off") or "momentary" (push-for "on" or push-for "off") type. A switch may be
directly manipulated by a human as a control signal to a system, such as a
computer keyboard button, or to control power flow in a circuit, such as a light
switch. Automatically operated switches can be used to control the motions of
machines, for example, to indicate that a garage door has reached its full open

position or that a machine tool is in a position to accept another workpiece.

Switches may be operated by process variables such as pressure, temperature,
flow, current, voltage, and force, acting as sensors in a process and used to
automatically control a system. For example, a thermostat is a temperatureoperated switch used to control a heating process. A switch that is operated by
another electrical circuit is called a relay. Large switches may be remotely
operated by a motor drive mechanism. Some switches are used to isolate electric
power from a system, providing a visible point of isolation that can be padlocked
if necessary to prevent accidental operation of a machine during maintenance, or
to prevent electric shock.
Contact terminology
In electronics, switches are classified according to the arrangement of
their contacts. A pair of contacts is said to be "closed" when current can flow from
one to the other. When the contacts are separated by an insulating air gap, they
are said to be "open", and no current can flow between them at normal voltages.
The terms "make" for closure of contacts and "break" for opening of contacts are
also widely used. In a switch where the contacts remain in one state unless
actuated, such as a push-button switch, the contacts can either be normally
open (abbreviated "n.o." or "no") until closed by operation of the switch, or
normally closed ("n.c." or "nc") and opened by the switch action. A switch with
both types of contact is called a changeover switch. These may be "makebefore-break" ("MBB" or shorting) which momentarily connects both circuits, or
may be "break-before-make" ("BBM" or non-shorting) which interrupts one
circuit before closing the other. The terms pole and throw are also used to
describe switch contact variations. The number of "poles" is the number of
separate circuits which are controlled by a switch. For example, a "2-pole" switch
has two separate identical sets of contacts controlled by the same knob. The
number of "throws" is the number of separate positions that the switch can adopt.
A single-throw switch has one pair of contacts that can either be closed or open.
A double-throw switch has a contact that can be connected to either of two other
contacts, a triple-throw has a contact which can be connected to one of three
other contacts, etc. These terms have given rise to abbreviations for the types of
switch which are used in the electronics industry such as "single-pole, single-

throw" (SPST) (the simplest type, "on or off") or "single-pole, double-throw"

(SPDT), connecting either of two terminals to the common terminal.
Electronics

Expansion

British American

specification

of

mains electrical

and

abbreviation wiring wiring

abbreviation

Description

name name
Equivalent
two

DPDT

Symbol

Double

pole,

double throw

to
SPDT

switches
controlled by a
single
mechanism.

Contact bounce
Contact bounce (also called chatter) is a common problem with
mechanical switches and relays. Switch and relay contacts are usually made of
springy metals. When the contacts strike together, their momentum and elasticity
act together to cause them to bounce apart one or more times before making
steady contact. The result is a rapidly pulsed electric current instead of a clean
transition from zero to full current. The effect is usually unimportant in power
circuits, but causes problems in some analogue and logic circuits that respond
fast enough to misinterpret the on-off pulses as a data stream. The effects of
contact bounce can be eliminated by use of mercury-wetted contacts, but these
are now infrequently used because of the hazard of mercury release.
Alternatively, contact circuits can be low-pass filtered to reduce or eliminate
multiple pulses. In digital systems, multiple samples of the contact state can be
taken or a time delay can be implemented in order for the contact bounce to
settle before the contact input is used to control anything. One way to implement
this with an SPDT Switch is by using an SR Latch.[7] These are referred to as
"debouncing" circuits.By analogy, the term "debounce" has arisen in the software
development industry to describe rate-limiting or throttling the frequency of a
method's execution.

Arcs and quenching

When the power being switched is sufficiently large, the electron flow
across opening switch contacts is sufficient to ionize the air molecules across the
tiny gap between the contacts as the switch is opened, forming a gas plasma,
also known as an electric arc. The plasma is of low resistance and is able to
sustain power flow, even with the separation distance between the switch
contacts steadily increasing. The plasma is also very hot and is capable of
eroding the metal surfaces of the switch contacts. Electric current arcing causes
significant degradation of the contacts and also significant electromagnetic
interference (EMI), requiring the use of arc suppression methods. Where the
voltage is sufficiently high, an arc can also form as the switch is closed and the
contacts approach. If the voltage potential is sufficient to exceed the breakdown
voltage of the air separating the contacts, an arc forms which is sustained until
the switch closes completely and the switch surfaces make contact. In either
case, the standard method for minimizing arc formation and preventing contact
damage is to use a fast-moving switch mechanism, typically using a springoperated tipping-point mechanism to assure quick motion of switch contacts,
regardless of the speed at which the switch control is operated by the user.
Movement of the switch control lever applies tension to a spring until a tipping
point is reached, and the contacts suddenly snap open or closed as the spring
tension is released. As the power being switched increases, other methods are
used to minimize or prevent arc formation. A plasma is hot and will rise due to
convection air currents. The arc can be quenched with a series of nonconductive
blades spanning the distance between switch contacts, and as the arc rises its
length increases as it forms ridges rising into the spaces between the blades,
until the arc is too long to stay sustained and is extinguished. A puffer may be
used to blow a sudden high velocity burst of gas across the switch contacts,
which rapidly extends the length of the arc to extinguish it quickly. Extremely
large switches in excess of 100,000-watt capacity often have switch contacts
surrounded by something other than air to more rapidly extinguish the arc. For
example, the switch contacts may operate in a vacuum, immersed in mineral oil,
or in sulfur hexafluoride. In AC power service, the current periodically passes
through zero; this effect makes it harder to sustain an arc on opening.

Manufacturers may rate switches with lower voltage or current rating when used
in DC circuits.
Power switching
When a switch is designed to switch significant power, the transitional
state of the switch as well as the ability to withstand continuous operating
currents must be considered. When a switch is in the on state, its resistance is
near zero and very little power is dropped in the contacts; when a switch is in the
off state, its resistance is extremely high and even less power is dropped in the
contacts. However, when the switch is flicked, the resistance must pass through
a state where a quarter of the load's rated power (or worse if the load is not
purely resistive) is briefly dropped in the switch. For this reason, power switches
intended to interrupt a load current have spring mechanisms to make sure the
transition between on and off is as short as possible regardless of the speed at
which the user moves the rocker. Power switches usually come in two types. A
momentary on-off switch (such as on a laser pointer) usually takes the form of a
button and only closes the circuit when the button is depressed. A regular on-off
switch (such as on a flashlight) has a constant on-off feature. Dual-action
switches incorporate both of these features.
Inductive loads
When a strongly inductive load such as an electric motor is switched off,
the current cannot drop instantaneously to zero; a spark will jump across the
opening contacts. Switches for inductive loads must be rated to handle these
cases. The spark will cause electromagnetic interference if not suppressed; a
snubber network of a resistor and capacitor in series will quell the spark.
Incandescent loads
When turned on, an incandescent lamp draws a large inrush current of
about ten times the steady-state current; as the filament heats up, its resistance
rises and the current decreases to a steady-state value. A switch designed for an
incandescent lamp load can withstand this inrush current.

Wetting current
Wetting current is the minimum current needing to flow through a
mechanical switch while it is operated to break through any film of oxidation that
may have been deposited on the switch contacts. [12] The film of oxidation occurs
often in areas with high humidity. Providing a sufficient amount of wetting current
is a crucial step in designing systems that use delicate switches with small
contact pressure as sensor inputs. Failing to do this might result in switches
remaining electrically "open" due to contact oxidation.
Actuator
The moving part that applies the operating force to the contacts is called
the actuator, and may be a toggle or dolly, a rocker, a push-button or any type
of mechanical linkage (see photo).
Biased switches
The momentary push-button switch is a type of biased switch. The most
common type is a "push-to-make" (or normally-open or NO) switch, which makes
contact when the button is pressed and breaks when the button is released.
Each key of a computer keyboard, for example, is a normally-open "push-tomake" switch. A "push-to-break" (or normally-closed or NC) switch, on the other
hand, breaks contact when the button is pressed and makes contact when it is
released. An example of a push-to-break switch is a button used to release a
door held closed by an electromagnet. The interior lamp of a household
refrigerator is controlled by a switch that is held open when the door is closed.
Toggle switch
A toggle switch is a class of electrical switches that are manually actuated
by a mechanical lever, handle, or rocking mechanism. Toggle switches are
available in many different styles and sizes, and are used in countless
applications. Many are designed to provide the simultaneous actuation of
multiple sets of electrical contacts, or the control of large amounts of electric
current or mains voltages. The word "toggle" is a reference to a kind of
mechanism or joint consisting of two arms, which are almost in line with each

other, connected with an elbow-like pivot. However, the phrase "toggle switch" is
applied to a switch with a short handle and a positive snap-action, whether it
actually contains a toggle mechanism or not. Similarly, a switch where a definitive
click is heard, is called a "positive on-off switch". Multiple toggle switches may be
mechanically interlocked to prevent forbidden combinations.
Special types
Switches can be designed to respond to any type of mechanical stimulus:
for example, vibration (the trembler switch), tilt, air pressure, fluid level (a float
switch), the turning of a key (key switch), linear or rotary movement (a limit switch
or microswitch), or presence of a magnetic field (the reed switch). Many switches
are operated automatically by changes in some environmental condition or by
motion of machinery. A limit switch is used, for example, in machine tools to
interlock operation with the proper position of tools. In heating or cooling systems
a sail switch ensures that air flow is adequate in a duct. Pressure switches
respond to fluid pressure.
Mercury tilt switch
The mercury switch consists of a drop of mercury inside a glass bulb with
2 or more contacts. The two contacts pass through the glass, and are connected
by the mercury when the bulb is tilted to make the mercury roll on to them. This
type of switch performs much better than the ball tilt switch, as the liquid metal
connection is unaffected by dirt, debris and oxidation, it wets the contacts
ensuring a very low resistance bounce-free connection, and movement and
vibration do not produce a poor contact. These types can be used for precision
works. It can also be used where arcing is dangerous (such as in the presence of
explosive vapour) as the entire unit is sealed.
Knife switch
Knife switches consist of a flat metal blade, hinged at one end, with an
insulating handle for operation, and a fixed contact. When the switch is closed,
current flows through the hinged pivot and blade and through the fixed contact.
Such switches are usually not enclosed. The knife and contacts are typically
formed of copper, steel, or brass, depending on the application. Fixed contacts

may be backed up with a spring. Several parallel blades can be operated at the
same time by one handle. The parts may be mounted on an insulating base with
terminals for wiring, or may be directly bolted to an insulated switch board in a
large assembly. Since the electrical contacts are exposed, the switch is used only
where people cannot accidentally come in contact with the switch or where the
voltage is so low as to not present a hazard. Knife switches are made in many
sizes from miniature switches to large devices used to carry thousands of
amperes. In electrical transmission and distribution, gang-operated switches are
used in circuits up to the highest voltages. The disadvantages of the knife switch
are the slow opening speed and the proximity of the operator to exposed live
parts. Metal-enclosed safety disconnect switches are used for isolation of circuits
in industrial power distribution. Sometimes spring-loaded auxiliary blades are
fitted which momentarily carry the full current during opening, then quickly part to
rapidly extinguish the arc.
Footswitch
A footswitch is a rugged switch which is operated by foot pressure. An
example of use is in the control of a machine tool, allowing the operator to have
both hands free to manipulate the workpiece. The foot control of an electric guitar
is also a footswitch.
Reversing switch
A DPDT switch has six connections, but since polarity reversal is a very
common usage of DPDT switches, some variations of the DPDT switch are
internally wired specifically for polarity reversal. These crossover switches only
have four terminals rather than six. Two of the terminals are inputs and two are
outputs. When connected to a battery or other DC source, the 4-way switch
selects from either normal or reversed polarity. Such switches can also be used
as intermediate switches in a multiway switching system for control of lamps by
more than two switches.
Light switches
In building wiring, light switches are installed at convenient locations to
control lighting and occasionally other circuits. By use of multiple-pole switches,

multiway switching control of a lamp can be obtained from two or more places,
such as the ends of a corridor or stairwell. A wireless light switch allows remote
control of lamps for convenience; some lamps include a touch switch which
electronically controls the lamp if touched anywhere. In public buildings several
types of vandal resistant switches are used to prevent unauthorized use.
Electronic switches
A relay is an electrically operated switch. Many relays use an
electromagnet to operate a switching mechanism mechanically, but other
operating principles are also used. Solid-state relays control power circuits with
no moving parts, instead using a semiconductor device to perform switching
often a silicon-controlled rectifier or triac. The analogue switch uses two
MOSFET transistors in a transmission gate arrangement as a switch that works
much like a relay, with some advantages and several limitations compared to an
electromechanical relay. The power transistor(s) in a switching voltage regulator,
such as a power supply unit, are used like a switch to alternately let power flow
and block power from flowing. Many people use metonymy to call a variety of
devices "switches" that conceptually connect or disconnect signals and
communication paths between electrical devices, analogous to the way
mechanical switches connect and disconnect paths for electrons to flow between
two conductors. Early telephone systems used an automatically operated
Strowger switch to connect telephone callers; telephone exchanges contain one
or more crossbar switches today. Since the advent of digital logic in the 1950s,
the term switch has spread to a variety of digital active devices such as
transistors and logic gates whose function is to change their output state
between two logic levels or connect different signal lines, and even computers,
network switches, whose function is to provide connections between different
ports in a computer network.[14] The term 'switched' is also applied to
telecommunications networks, and signifies a network that is circuit switched,
providing dedicated circuits for communication between end nodes, such as the
public switched telephone network. The common feature of all these usages is
they refer to devices that control a binary state: they are either on or off, closed
or open, connected or not connected.

Power supply

A regulated power supply is an embedded circuit; it converts

unregulated AC into a constant DC. With the help of a rectifier it converts AC
supply into DC. Its function is to supply a stable voltage (or less often current),
to a circuit or device that must be operated within certain power supply limits.
The output from the regulated power supply may be alternating or unidirectional,
but is nearly always DC (Direct Current).
The type of stabilization used may be restricted to ensuring that the output
remains within certain limits under various load conditions, or it may also include
compensation for variations in its own supply source. The latter is much more
common today.

D.C. variable bench supply (a bench power supply usually refers to a

power supply capable of supplying a variety of output voltages useful for
bench testing electronic circuits, possibly with continuous variation of the
output voltage, or just some preset voltages; a laboratory (lab) power
supply normally implies an accurate bench power supply, while a balanced
or tracking power supply refers to twin supplies for use when a circuit
requires both positive and negative supply rails).

Mobile Phone power adaptors

Regulated power supplies in appliances

Various amplifiers and oscillators

Many topologies have been used since the regulated supply was invented.
Early

technologies

included

iron-hydrogen

resistors,

resonant

transformers, nonlinear resistors, loading resistors, neon stabiliser tubes,

vibrating contact regulators etc.

Modern regulated supplies mostly use a transformer, silicon diode bridge

recitifer, reservoir capacitor and voltage regulator IC. There are variations
on this theme, such as supplies with multiple voltage lines, variable
regulators, power control lines, discrete circuits and so on. Switched mode
regulator supplies also include an inductor.

At times regulated supplies can be much more complex. An example

supply from a 1980s TV used bidirectional interaction between the main
supply and the line output stage to operate, generating a range of output

voltages with varying amounts of stabilisation. Since neither stage could

start without the other running, the supply also included a kickstart system
to pulse the system into operation. The supply also monitored voltages in
the TV power circuitry, shutting down if these voltages went out of spec.
For special applications, supplies can become even more complex.

PLYWOOD
Foam board is a very strong, lightweight, and easily cut material used for
the mounting of photographic prints, as backing in picture framing, in 3D design,
and in painting. It is also in a material category referred to as "Paper-faced
Foam Board". It consists of three layers an inner layer of polystyrene foam
clad with outer facing of either a white claycoated paper or brown kraft paper.
The surface of the regular board, like many other types of paper, is slightly
acidic. However for modern archival picture framing and art mounting purposes
it can be produced in a neutral, acid-free version with a buffered surface paper,
in a wide range of sizes and thicknesses. Foam-cored materials are also now
available with a cladding of solid (non-foamed) polystyrene and other rigid
plastic sheeting, some with a textured finish. Foamcore does not adhere well to
some glues, such as superglue, and certain types of paint. The foam tends to
melt away and dissolve. Some glue works well in casual settings, however, the
water in the glue can warp the fibers in the outer layers. Best results are
typically obtained from higher-end spray adhesives. A hot glue gun can be used
as a substitute, although the high viscosity of hot glues can affect finished
projects in the form of board warping, bubbles, or other unsightly blemishes.
Self-adhesive foam boards, intended for art and document mounting are also
available, though these can be very tricky to use properly; this is because the
glue sets very fast. It is considered cheaper to buy plain foam board and then
re-positionable spray mount adhesive. Foamcore is commonly used to produce
architectural models, prototype small objects and to produce patterns for
casting. Scenery for scale model displays, dioramas, and computer games are
often produced by hobbyists from foamcore. It's also often used by
photographers as a reflector, in the design industry to mount presentations of
new products, and in picture framing as a backing material; the latter use
includes some archival picture framing methods, which utilize the acid-free
versions of the material. Another use is with aero-modellers for building radiocontrolled aircraft.

Square tube
Hollow square tube, which have a uniform cross-section with only one
enclosed void along their whole length in the shape of rectangles (including
squares), and which have a uniform wall thickness.

Hack saw
A cutting blade is a fine-tooth hand saw with a blade held under tension
in a frame, used for cutting materials such as metal or plastics. Hand-held cutting
blades consist of a metal arch with a handle, usually a pistol grip, with pins for
attaching a narrow disposable blade. A screw or other mechanism is used to put
the thin blade under tension. The blade can be mounted with the teeth facing
toward or away from the handle, resulting in cutting action on either the push or
pull stroke. On the push stroke, the arch will flex slightly, decreasing the tension
on the blade, often resulting in an increased tendency of the blade to buckle and
crack. Cutting on the pull stroke increases the blade tension and will result in
greater control of the cut and longer blade life.
Blades are available in standardized lengths, usually 10 or 12 inches for a
standard hand cutting blade. "Junior" cutting blades are half this size. Powered
cutting blades may use large blades in a range of sizes, or small machines may
use the same hand blades.
The pitch of the teeth can be anywhere from fourteen to thirty-two teeth
per inch (tpi) for a hand blade, with as few as three tpi for a large power cutting
blade blade. The blade chosen is based on the thickness of the material being
cut, with a minimum of three teeth in the material. As cutting blade teeth are so
small, they are set in a "wave" set. As for other saws they are set from side to
side to provide a kerf or clearance when sawing, but the set of a cutting blade
changes gradually from tooth to tooth in a smooth curve, rather than alternate
teeth set left and right.
Cutting blade blades are normally quite brittle, so care needs to be taken
to prevent brittle fracture of the blade. Early blades were of carbon steel, now
termed 'low alloy' blades, and were relatively soft and flexible. They avoided
breakage, but also wore out rapidly. Except where cost is a particular concern,

this type is now obsolete. 'Low alloy' blades are still the only type available for the
Junior cutting blade, which limits the usefulness of this otherwise popular saw.
For several decades now, cutting blade blades have used high speed
steel for their teeth, giving greatly improved cutting and tooth life. These blades
were first available in the 'All-hard' form which cut accurately but were extremely
brittle. This limited their practical use to benchwork on a workpiece that was
firmly clamped in a vice. A softer form of high speed steel blade was also
available, which wore well and resisted breakage, but was less stiff and so less
accurate for precise sawing. Since the 1980s, bi-metal blades have been used to
give the advantages of both forms, without risk of breakage. A strip of high speed
steel along the tooth edge is electron beam welded to a softer spine. As the price
of these has dropped to be comparable with the older blades, their use is now
almost universal.
Cutting blade blade specifications: The most common blade is the 12
inch or 300 mm length. Cutting blade blades have two holes near the ends for
mounting them in the saw frame and the 12 inch / 300 mm dimension refers to
the center to center distance between these mounting holes. [1]
12 Inch Blade:
Hole to Hole: 11 7/8 inches / 300 mm
Overall blade length: 12 3/8 inches / 315 mm (not tightly controlled)
Mounting Hole diameter: 9/64 to 5/32 inch / 3.5 to 4 mm (not tightly controlled)
Blade Width: 7/16 to 33/64 inch / 11 to 13 mm (not tightly controlled)
Blade Thickness: 0.020 to 0.027 inches / 0.5 to 0.70 mm (varies with tooth pitch
and other factors)
The kerf produced by the blades is somewhat wider than the blade
thickness due to the set of the teeth. It commonly varies between 0.030 and
0.063 inches / 0.75 and 1.6 mm depending on the pitch and set of the teeth.

The 10 inch blade is also fairly common and all the above dimensions
apply except for the following:
Hole to Hole: 9 7/8 inches / 250 mm
Overall blade length: 10 3/8 inches / 265 mm (not tightly controlled)
A panel cutting blade eliminates the frame, so that the saw can cut into panels of
sheet metal without the length of cut being restricted by the frame.
Junior cutting blades are the small variant, while larger mechanical cutting blades
are used to cut working pieces from bulk metal.
A power cutting blade (or electric cutting blade) is a type of cutting blade
that is powered either by its own electric motor or connected to a stationary
engine. Most power cutting blades are stationary machines but some portable
models do exist. Stationary models usually have a mechanism to lift up the saw
blade on the return stroke and some have a coolant pump to prevent the saw
blade from overheating.
While stationary electric cutting blades are reasonably uncommon they
are still produced but saws powered by a stationary engines have gone out of
fashion. The reason for using one is that they provide a cleaner cut than an angle
grinder or other types of saw. Large, power cutting blades are sometimes used in
place of a bandsaw for cutting metal stock to length.

Nut
A nut is a type of fastener with a threaded hole. Nuts are almost always
used opposite a mating bolt to fasten a stack of parts together. The two partners
are kept together by a combination of their threads' friction, a slight stretch of the
bolt, and compression of the parts. In applications where vibration or rotation
may work a nut loose, various locking mechanisms may be employed:
Adhesives, safety pins or lockwire, nylon inserts, or slightly oval-shaped threads.
The most common shape is hexagonal, for similar reasons as the bolt head - 6
sides give a good granularity of angles for a tool to approach from (good in tight
spots), but more (and smaller) corners would be vulnerable to being rounded off.

Other specialized shapes exist for certain needs, such as wing nuts for finger
adjustment and captive nuts for inaccessible areas.
Nuts are graded with strength ratings compatible with their respective
bolts; for example, an ISO property class 10 nut will be able to support the bolt
proof strength load of an ISO property class 10.9 bolt without stripping. Likewise,
an SAE class 5 nut can support the proof load of an SAE class 5 bolt, and so on.
A wide variety of nuts exists, from household hardware versions to specialized
industry-specific designs that are engineered to meet various technical
standards.
Types

Acorn nut (cap nut)

Barrel nut

Cage nut

Clip-on nut (J-nut or U-nut)

Coupling nut

Cross dowel

Flange nut (collar nut)

Insert nut

Sex bolt

Slotted nut

Split nut

Sleeve nut

Square nut

Staked/welded nut (for plastic)

Swage nut

T-nut

T-slot nut (T-groove) nut

Weld nut

Well nut

Wing nut

Locknuts

Castellated nut

Distorted thread locknut

o

Centerlock nut

Elliptical offset locknut

Toplock nut

Interfering thread nut

o

Tapered thread nut

Jam nut

Jet nut (K-nut)

Keps nut (K-nut or washer nut) with a star-type lock washer

Nyloc plate nut

Polymer insert nut (Nyloc)

Serrated face nut

Serrated flange nut

Speed nut (Sheet metal nut or Tinnerman nut)

Split beam nut

Standard metric hex nuts sizes

flat (wrench) sizes differ from industry standards. For example, wrench
sizes of fastener used in Japanese built cars comply with JIS automotive
standard.
Use of two nuts to prevent self-loosening
In normal use, a nut-and-bolt joint holds together because the bolt is under
a constant tensile stress called the preload. The preload pulls the nut threads
against the bolt threads, and the nut face against the bearing surface, with a
constant force, so that the nut cannot rotate without overcoming the friction
between these surfaces. If the joint is subjected to vibration, however, the
preload increases and decreases with each cycle of movement. If the minimum
preload during the vibration cycle is not enough to hold the nut firmly in contact
with the bolt and the bearing surface, then the nut is likely to become loose.
Specialized locking nuts exist to prevent this problem, but sometimes it is
sufficient to add a second nut. For this technique to be reliable, each nut must be
tightened to the correct torque. The inner nut is tightened to about a quarter to a
half of the torque of the outer nut. It is then held in place by a wrench while the

outer nut is tightened on top using the full torque. This arrangement causes the
two nuts to push on each other, creating a tensile stress in the short section of
the bolt that lies between them. Even when the main joint is vibrated, the stress
between the two nuts remains constant, thus holding the nut threads in constant
contact with the bolt threads and preventing self-loosening. When the joint is
assembled correctly, the outer nut bears the full tension of the joint. The inner nut
functions merely to add a small additional force to the outer nut and does not
need to be as strong, so a thin nut (also called a jam nut) can be used.

Bolt
A screw, or bolt, is a type of fastener characterized by a helical ridge,
known as an external thread or just thread, wrapped around a cylinder. Some
screw threads are designed to mate with a complementary thread, known as an
internal thread, often in the form of a nut or an object that has the internal thread
formed into it. Other screw threads are designed to cut a helical groove in a
softer material as the screw is inserted. The most common uses of screws are to
hold objects together and to position objects.
A screw will always have a head, which is a specially formed section on
one end of the screw that allows it to be turned, or driven. Common tools for
driving screws include screwdrivers and wrenches. The head is usually larger
than the body of the screw, which keeps the screw from being driven deeper than
the length of the screw and to provide a bearing surface. There are exceptions;
for instance, carriage bolts have a domed head that is not designed to be driven;
set screws often have a head smaller than the outer diameter of the screw; Jbolts have a J-shaped head which is not designed to be driven, but rather is
usually sunk into concrete allowing it to be used as an anchor bolt. The
cylindrical portion of the screw from the underside of the head to the tip is known
as the shank; it may be fully threaded or partially threaded. [1] The distance
between each thread is called the "pitch". The majority of screws are tightened by
clockwise rotation, which is termed a right-hand thread; a common mnemonic
device for remembering this when working with screws or bolts is "righty-tighty,
lefty-loosey." Screws with left-hand threads are used in exceptional cases. For
example, when the screw will be subject to counterclockwise torque (which would
work to undo a right-hand thread), a left-hand-threaded screw would be an

appropriate choice. The left side pedal of a bicycle has a left-hand thread. More
generally, screw may mean any helical device, such as a clamp, a micrometer, a
ship's propeller or an Archimedes' screw water pump.

7
REFERENCES

REFERENCES
Website:
Google.com
Philips Semiconductor